Having considered ‘Poor Decisions’ and the millennia-old revulsion against killing, let our thoughts turn to murder. The Sixth Commandment of God gave humanity an early steer that murder is a bad thing.

Centuries of religious and moral codes have been reinforced by laws and penalties, backed up by law enforcement agencies which threaten a killer with the likelihood of punishment for his crimes (let alone eternal damnation). Not only is it a bad thing, but also a really, really bad idea.

All this results, thankfully, in a tiny proportion of a ‘civilised’ population being prepared to kill, and an even smaller number prepared to do so ‘in cold blood’. The UK Murder rate is 0.9 per 100,000 people per annum, even gun-toting USA scores just 3.6 and the killing is concentrated in certain areas and certain population groups (i.e. poor young men from inner cities, and tragically infants under 1 year). The murder rate has to be very low for a well-ordered society to continue; beyond a tipping point it’s Gun Law, and every man for himself. Guatemala, which I discussed in a previous blog, has 10 times the murder rate of the USA and feels like a war zone. On my island of Guernsey there’s one every few years, generally a ‘domestic’ or the unintended consequence of a drunken fight.

Most murders are committed in hot blood; following an argument, an irrational impulse, or a sudden burst of fear. In many cases the killer is not thinking straight, acting under the effect of drink, drugs or mental impairment. I am annoyed by books and especially films that overlook the block constructed by thousands of years of human experience which shows that being willing to kill can act against self-preservation. This is especially the case where a second person in the plot is also a one-in-10,000 killer. In a recent English ‘cosy’ I read there were no fewer than three people in a small village willing to kill without remorse.

Even under stress, most ordinary people will struggle to fire that gun or plunge that knife in self-defence ­– one reason that the claim that ‘I have a gun at home to protect my family’ is bollocks.

American police shot and killed 963 people in 2016, which is just over 1 person per 1,000 law enforcement officers. So in a 25-year career roughly 1 cop in 40 will kill someone. That doesn’t make very exciting TV, does it? It pushes many cop shows into the realm of fantasy. Last week we had the highly visible shooting dead of a terrorist by British police – remarkable not only for the terrifying 80 seconds that preceded it but for its rarity.

So how do my fellow crime-writers climb this wall? Ordinary housewives and vicars are not easily turned into murderers and policemen do not happily pull their guns and start shooting. A switch must be pulled, that block must be broken down. Writers need to work to convince the reader this has happened. The reader of murder-mystery will expect at least one murder; it’s part of the contract. Belief is therefore suspended to the benefit of the writer; the reader cuts us a little slack. The 700-plus members of the UK’s Crime Writer’s Association probably ‘kill’ more people annually than do actual criminals, but to be fair, science fiction writers also defeat more alien invasions than actually occur. Amid all this fictional mayhem the trick is then to keep it real, keep that killer’s motivation believable. Murder must be the only option available to our criminal at the split second it takes place, assuming he or she is of sound mind and capable of taking rational decisions. It can’t just be there to fulfil that contract; we must be convinced that the killer will break the oldest taboo: ‘Thou Shalt Not Kill’.

Jason Monaghan is speaking at the Guernsey Literary Festival on Friday 12 May.